Principle and animation of a pulse combustor

Following animation shows the gas temperature in the pulsed combustor, which is a computer-simulated 2D system without mechanical valves and with long tail pipe.

animatie pulse combustion

Fuel LPG and fresh air are flowing into the combustor (left side of picture). Colors indicating instantaneous gas temperature.

Color

Low Temp. (up to 800K)

Mid Temp. (800K to 1200K)

High Temp. (over 1200K)

Air

Fuel

Line in graph.

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pressure in combustion chamber

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heat release rate

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Entering air velocity

Let start to explain the cycle when the whole gas temperature is indicated as 'red'. This is when the exhaust gas at the exit has near zero speed, but the gas in the tailpipe begins to run toward upstream (to left), because of the decreasing pressure in the combustion chamber. The low pressure causes a recharge of fresh air/gas in the combustion chamber. Low temperature fresh mixture has not ingnited but is just flowing into the combustion chamber. It needs a higher temperature. This is realized by mixing with very hot burned gasses in the chamber. Then, at the interface of burned and unburned gas, and explosion will take place instantaneously because of the intense mixing. This is shown as 'yellow' color in above anamation.

The explosion pressure is pushing the gases into the inlet pipe towards the left side and into the exhaust tail pipe towards the right side. The gas in tail pipe will continue to flow toward the right but the gas in inlet pipe flow in reverse. This reversed gas has not a combustible mixture, when the flow direction turns to normal, the fresh air has to push out this exhaust gas to begin the next burning cycle. This will cause a delay which is important to keep oscillation of pulsation going.

The air/fuel has not mixed yet, it is mixed after the interaction with burned gas which residued in the combustion chamber. This is the reason why pulsed combution is called 'high temperature diluted combustion' and is complete burned with ultra low NOx emission, resulting in very clean combustion.